1. Field of the Invention
The present invention relates to an energy-absorbing unit which is particularly suited for use as an additional irreversible shock-absorbing stage together with a component for transferring force.
2. Description of the Related Art
Printed publication DE 297 03 351 U1 describes an element for absorbing kinetic energy, wherein said element works mechanically according to the plastic deformation principle. Specifically, this prior art proposes an energy-absorbing element including a base plate and a connecting plate, wherein an energy-absorbing element is fixed between these two plates. Said energy-absorbing element is a thick-walled plastic tube which on the one hand exhibits a certain initial elasticity and, on the other, an almost rectangular plastic working stroke. The initial elasticity of the absorption element yields deformation protection upon minor impacts. A plastic deformation of the section occurs after a working stroke beyond the yield strength, in consequence of which the section exhibits a reduced length with a bulged enlarged outer diameter.
The DE 747 330 C printed publication relates to a plunger buffer having an integrated energy-absorbing element. The conventional plunger buffer includes a buffer rod which, aided by a buffer bar and a buffer spring provided within said buffer rod, is affixed to the front end of a railcar body such that the buffer rod is capable of absorbing moderate impacts. After the maximum available damping stroke has been exhausted, the buffer plate strikes against a flange projecting into the front section of a deformation tube.
A buffer/drawgear mechanism including a telescoped arrangement of deformation tubes which plastically deform successively upon the operating load of the buffer/drawgear mechanism being exceeded is known from printed publication U.S. Pat. No. 3,428,150.
A damping element for a vehicle including at least one irreversibly-designed energy-absorbing element in the form of a deformation tube is known from printed publication GB 1 419 698 A.
Printed publication EP 0 826 569 A2 describes an impact protection device for railborne vehicles including a side buffer and an energy-absorbing unit downstream of said side buffer. Specifically, the energy-absorbing unit is in principle designed as a “crash box” detachably affixable at one side to the front end of the railcar body while the side buffer can likewise be detachably affixed to the other side of the crash box. This prior art explicitly teaches using a box-shaped crash box tapering toward the side buffer as the energy-absorbing unit so as to enable the most controlled possible buckling of the energy-absorbing element in the event of a crash.
It is therefore, generally known in the field of rail vehicle technology, to equip for example, the individual car bodies of a multi-member vehicle, with so-called side buffers or International Union of Railways (UIC) buffers when the car bodies are not connected together by a bogie and thus, the distance between the two coupled car bodies can vary during normal vehicle operation. These side buffers thereby serve to absorb and dampen impacts occurring during normal vehicle operation, for example when braking or bringing up to speed.
A telescoped structure is normally utilized for the side buffer which includes a buffer housing, a force-transferring member accommodated therein and a damping element in the form of a spring or an elastomer body. With this type of structure, the buffer housing serves as a longitudinal guide and for the supporting of transverse forces while the damping element accommodated in the buffer housing serves in transferring force in the longitudinal direction.
The overall length as well as the buffer stroke; i.e., the spring travel of the damping element, is standardized for certain vehicle categories by European regulations (e.g., the UIC 526 and 528 leaflets). The buffer stroke for a standardized UIC buffer, for example, is within a range of from 100 to 110 mm. After reaching maximum buffer stroke, the damping characteristic of the side buffer is exhausted, in consequence of which impact forces which exceed the characteristic operating load of the side buffer are routed to the vehicle undercarriage undampened.
While the impact forces which occur during normal operation of the vehicle, for example, between individual car bodies of a multi-member vehicle, are thus, absorbed by the regeneratively-designed damping element integrated in the side buffer, when the operating load of the side buffer is exceeded, however, for instance when the vehicle collides with an obstacle or when the vehicle is abruptly braked, the damping element integrated in the side buffer is usually unable to absorb the total resulting energy. The shock absorbance provided by the side buffer is thus, no longer integrated into the energy-absorbing concept of the vehicle as a whole, such that the resulting impact forces are transmitted directly to the vehicle undercarriage. This subjects same to extreme loads with the potential to damage or even destroy same.
With the goal of preventing such damage, it is conventionally known to design the guiding members of the plunger buffer such that after the maximum buffer stroke has been exhausted; i.e., after the guiding members of the side buffer (buffer sleeve and buffer rod) strike defined arresters, there is an additional contracting possibility with controlled deformation.
For example, the WO 2005/115818 A1 printed publication describes a plunger buffer in which after the energy absorption provided by the regeneratively-designed damping element has been exhausted, predetermined break joints break away so as to thus increase the contracting length of the buffer. This increased contracting length allows the plastic deformation of the buffer housing upon overload so that this solution enables a destructive conversion of impact energy into the work of deformation and heat. The resulting deformation of the buffer housing which occurs upon overload thus provides an additional protection against impacts to the shock absorbance provided by the side buffer.
Even if this side buffer known in the art can protect the vehicle undercarriage up to a certain degree from damage upon severe collisions, it is thereby not possible to adapt the additional shock absorber to specific applications. To do so would require commensurately designing the force-path characteristic for the deformation of the buffer housing so as to enable a predictable, defined absorption of energy. In particular, the known solution is unsuited for many applications since the maximum energy absorption achievable with the deformation of the buffer housing is often too low.
A further disadvantage can be seen in the fact that after the additional shock absorber has been activated, the entire side buffer needs to be replaced since the shock absorber is integrated in the side buffer and because due to the at least partial deformation of the buffer housing, the side buffer can no longer be used in normal vehicle operation.